Intercritical Heat Treatment Effects on Low Carbon Steels Quenched from Intermediate Temperature Austenitization

Abstract

Six low carbon steels containing carbon in the range 0.13-0.18wt%C were studied after intercritical quenching, intercritical quenching with low temperature tempering, intercritical annealing and intercritical normalizing using specimens originally quenched from intermediate austenitizing temperature (950⁰C). The studies also examined the microstructure of the intermediate austenitizing temperature (950⁰C) quenched specimens. The intercritical and tempering temperatures were 740⁰C and 180⁰C respectively. Comparison of the mechanical properties of the intercritically heat treated specimens with those of the intermediate austenitizing temperature specimens showed that intercritical quenching with low temperature tempering reduced the ultimate tensile strength and hardness  and increased the percentage reduction in area and the notch impact toughness. Intercritical annealing and intercritical normalizing increased the yield strength, ductility and toughness but decreased the ultimate tensile strength and hardness.